1. Field of the Invention
The present invention generally relates to an image forming apparatus using an electrophotographic system, a cartridge detachably mountable to a main body of the image forming apparatus, which is to say a process cartridge, and to a developing apparatus constructed as a cartridge.
In this case, examples of the electrophotographic image forming apparatus include an electrophotographic copying machine, an electrophotographic printer (for instance, an LED printer, a laser beam printer, and the like), an electrophotographic facsimile apparatus, and the like.
Also, the cartridge detachably mountable to the main body of the electrophotographic image forming apparatus is a cartridge including at least one of an electrophotographic photosensitive body, a charging means for charging the electrophotographic photosensitive body, a developing means for supplying developer to the electrophotographic photosensitive body, and a cleaning means for cleaning the electrophotographic photosensitive body. In particular, the process cartridge integrally combines the electrophotographic photosensitive body with at least one of the charging means, the developing means, and the cleaning means into a cartridge detachably mountable to the main body of the electrophotographic photosensitive body. Alternatively, the process cartridge integrally combines at least the developing means with the electrophotographic photosensitive body into a cartridge detachably mountable to the main body of the electrophotographic image forming apparatus.
2. Related Background Art
An example of a conventional electrophotographic image forming apparatus is shown in FIG. 12. In this drawing, the image forming apparatus includes a photosensitive drum 101 as an electrophotographic photosensitive body to which an organic photosensitive body (organic photo-conductor) is applied or a photo-conductive body made of Axe2x80x94Si, Cds, Se, or the like on the outer peripheral surface of an aluminum cylinder. This photosensitive drum 101 is driven by an unillustrated driving means in a direction indicated by the illustrated arrow and is uniformly charged at a predetermined potential by a roller charger 102 that is a charging means.
In the upper portion of the main body of the apparatus, there are disposed a laser diode 111 that constitutes an exposing apparatus as an electrostatic latent image forming means, a polygon mirror 109 that is rotatably driven by a high speed motor 108, a lens 110, and a return mirror 107.
When an image signal is inputted into a laser driver 112, the laser driver 112 causes the laser diode 111 emit light. Then, the light having optical information corresponding to the image signal travels along an optical path 113 and irradiates the photosensitive drum 101, thereby forming an electrostatic latent image. Further, when the photosensitive drum 101 is rotated in the arrow direction, this electrostatic latent image is developed by a developing apparatus (developing means) 104, thereby obtaining a toner visible image. The toner visible image obtained by the development is transferred onto transferring paper P, which is a transferring material, by a transferring roller 103 that is a transferring means to which a predetermined bias is applied. The transferring paper P is conveyed by a convey means to a fixing apparatus 105, and the toner visible image is melted and fixed by the fixing apparatus 105. In this manner, there is obtained a permanent image.
On the other hand, residual toner on the photosensitive drum 101 is removed by a cleaning apparatus 106 such as a fur brush or a blade means.
By the way, in an image forming apparatus that uses an electrophotographic system and outputs a gradation image, there generally exists a relation between inputted image signals and outputted images, that is, there exists a gradation characteristic, as shown in FIG. 13. If this default gradation characteristic is used as it is, it is impossible to obtain a high-quality image in the usual cases. Therefore, in actual cases, before being inputted into the laser driver 112, the image signals are adjusted by referring to a look-up table (hereinafter referred to as the xe2x80x9cLUTxe2x80x9d) formed in a RAM within a memory 121 so that the gradation characteristic becomes an appropriate relation such as a linear relation. To do so, halftone control is performed by experimentally forming toner images (hereinafter referred to as the xe2x80x9cpatch patternsxe2x80x9d) used to detect image densities on the photosensitive drum 101 from all image signals that can be dealt with, detecting densities of these toner images using an optical density sensor 122 or the like, obtaining a present gradation characteristic of the image forming apparatus from the detection results, and creating an LUT according to the obtained present gradation characteristic. This makes it possible to obtain a desired gradation characteristic with precision.
In more detail, in FIG. 12, a CPU 120 inputs signals for forming the patch patterns into the laser driver 112, and then visualized images are formed on the photosensitive drum 101. The optical density sensor 122 detects the visualized images, and an LUT is created in the RAM within the memory 121 functioning as a storage means according to the detection results.
By detecting the patch patterns formed on the photosensitive drum 101 using the optical density sensor 122 in this manner, it becomes possible to directly correct the relations between image signals and images formed on the photosensitive drum 101 using the LUT. However, images that are finally obtained the are images transferred from the photosensitive drum 101 onto the transferring paper P. Therefore, in actual cases, with consideration given to a transfer efficiency during this image transfer, correction amounts given by the LUT are determined so that there can be finally obtained correct relations between the image signals and the images on the transferring paper P.
Also, the correction performed using the LUT is a halftone correction and therefore, if the maximum value of a density of an image to be printed varies, it becomes difficult to perform correction using the LUT. In view of this problem, there is used a method with which prior to the halftone correction, a patch pattern used to detect the maximum density is additionally formed on the photosensitive drum 101 and a developing bias voltage applied to the developing apparatus 104 and a bias voltage applied to the charging means 102 for charging the photosensitive drum 101 are adjusted according to a detection result of the patch pattern. In this manner, the maximum density is corrected.
In actual cases, like the halftone correction, this maximum density correction is also performed by determining a target value for the density of the patch pattern on the photosensitive drum 101 with consideration given to the transfer efficiency during the final transfer of the toner image onto the transferring paper P.
However, if the density detection is performed by forming a patch pattern at a place other than the transferring paper P in this manner, when the transfer efficiency to the transferring paper P varies due to endurance, that is, due to an extended period of use of the apparatus, there occurs a problem that even though the toner image density on the photosensitive drum 101 is properly corrected, the final image on the transferring paper varies due to the endurance.
In particular, in the case of a full-color image forming apparatus that forms a full-color image using toner in four colors, variations of halftone densities result in variations of hues. Consequently, the stated problem becomes more serious than in a case of a monochrome image forming apparatus.
As a method of preventing this problem, there is a method with which the halftone correction and the maximum density correction described above are performed by directly transferring the aforementioned patch patterns onto transferring paper and detecting these patterns after transfer, more preferably after fixation.
In this case, however, there occurs a problem that the transferring paper P is additionally consumed each time the density correction is performed and therefore this method is not economical.
Therefore, an object of the present invention is to provide an image forming apparatus and a cartridge which can economically perform image density control with stability at all times for a long period of time.
The above-mentioned object is attained by an image forming apparatus and a cartridge according to the present invention. In short, the present invention provides an image forming apparatus, to which a cartridge including at least a developing means is detachably mountable, comprising: an image control means for adjusting an image on a transferring material by directly detecting the density of a toner image formed on an image bearing body or by transferring the toner image onto a second image bearing body and detecting the density of the transferred toner image, characterized in that a control parameter of the image control means is changed according to the degree of wear of the cartridge.
According to one aspect of the present invention, in the image forming apparatus, a correction parameter is stored and held in advance in a storage means mounted in the cartridge, the correction parameter being used to determine, according to the degree of wear of the cartridge, the degree to which the control parameter of the image control means should be changed.
According to another aspect of the present invention, in the image forming apparatus, the control parameter of the image control means is an image forming condition after image control is performed. According to another aspect of the present invention, in the image forming apparatus, the control parameter of the image control means is a target density during image control.
According to another aspect of the present invention, in the image forming apparatus, the control parameter of the image control means is a density conversion table that is used when the toner image on the image bearing body is detected during image control. According to another aspect of the invention, in the image forming apparatus, the control parameter of the image control means is a look-up table that is used during halftone control.
According to another aspect of the present invention, in the image forming apparatus, the control parameter of the image control means is a condition concerning transfer of a density detection toner image onto the second image bearing body, the transfer being performed in a case where image control is performed by forming the density detection toner image on the image bearing body using the developing means, transferring the density detection toner image onto the second image bearing body, and detecting the density of the transferred density detection toner image.
According to another aspect of the present invention, there is provided a cartridge that includes at least a developing means and is detachably mountable to a color image forming apparatus including an image control means for adjusting an image on a transferring material by directly detecting the density of a toner image formed on an image bearing body or by transferring the toner image onto a second image bearing body and detecting a density of the transferred toner image. The cartridge comprises: a storage means, in which a correction parameter is stored and held in the storage means, the correction parameter being used to determine, according to the degree of wear of the cartridge, the degree to which a control parameter of the image control means should be changed.
According to another aspect of the invention, in the above-mentioned aspects, the degree of wear of the cartridge is sequentially stored in the storage means.
According to another aspect of the invention, in the above-mentioned aspects, the cartridge is a process cartridge that further integrally includes an electrophotographic photosensitive body that is the image bearing body; and at least one of a charging means for charging the electrophotographic photosensitive body and a cleaning means for cleaning the electrophotographic photosensitive body.
With the technique of the present invention, there is realized an image forming apparatus to which a cartridge including at least a developing means is detachably mountable, the image forming apparatus comprising: an image control means for adjusting an image on a transferring material either by directly detecting the density of a toner image formed on an image bearing body or by transferring the toner image onto a second image bearing body and detecting the density of the transferred toner image, wherein a control parameter of the image control means is changed according to the degree of wear of the cartridge. With this construction, it becomes possible to economically perform image density control with stability at all times. In addition, this effect lasts for a long time. This makes it possible to obtain high-quality images at all times.
Also, there is realized a cartridge that includes at least a developing means and is detachably mountable to a color image forming apparatus including an image control means for adjusting an image on a transferring material either by directly detecting the density of a toner image formed on an image bearing body or by transferring the toner image onto a second image bearing body and detecting the density of the transferred toner image, the cartridge comprising a storage means, wherein a correction parameter is stored and held in the storage means, the correction parameter being used to determine, according to the degree of wear the cartridge, the degree to which a control parameter of the image control means should be changed. This construction contributes to making it possible to economically perform image density control with stability at all times. In addition, this effect lasts for a long time. This construction also contributes to making it possible to obtain high-quality images at all times.
These and other objects and advantages of the invention may be readily ascertained by referring to the following description and accompanying drawings.